just finished

Cinderella, the question is why did you think a Z curve would work in the first place? No curve can work for all images. You need to understand the "numbers" in your image, determine whether it needs a global correction or specific areas and build a Curve to fix those weaknesses. Look again at Edgework's post. He built something very specific based on his analysis of the original pic. Might be interesting to see your pic and what the problem is although you should start a new post.